Why Polarity Switching Matters

The Basics
In today’s busy analytical laboratories, productivity and high sample throughput are constant demands. More samples need to be analyzed in a shorter timeframe. Laboratories must work to use equipment at its maximum capacity, and methods must be optimized.

With liquid chromatography-mass spectrometry (LC-MS), the chromatography separation has the capacity to resolve a certain number of compounds in a specified period of time. Generally, the shorter the LC run time, the poorer the chromatographic resolution. This potentially affects the MS data quality for those analytes. This is true even for high capacity LC columns, such as those for ultra-high-performance liquid chromatography (UHPLC). 

With an MS detector—let’s say a triple quadrupole MS—you can overcome some of the chromatography shortfalls by using a highly-specific data acquisition method such as Selected Reaction Monitoring (SRM). This is also known as Multiple Reaction Monitoring (MRM) when more than one reaction is involved. The approach allows compounds to be identified and tracked by a specific precursor to product ion transition, or MRM. As the term “multiple” suggests, you can run concurrent compound transitions in virtually the same time frame (within a few milliseconds). Because each transition is unique to a compound, MRM is a highly specific, sensitive, and efficient way of quantifying an analyte.

With a SCIEX triple quadrupole, the unique features of the acquisition software allow the method to be finely optimized to achieve the right number of data points for accurate and precise quantification of chromatographic peaks. This is a feature called Scheduled MRM™ Pro algorithm. It provides a very efficient way of analyzing 100s of analytes within the necessary duty cycle.

The Polarity Question
What if you need a single LC-MS/MS method to analyze compounds with positive and negative ionization states simultaneously? And what if you need to look at both ionization modes while maintaining a high duty cycle, high selectivity, high sensitivity, and chromatographic peak shape integrity?

Well, MS instruments such as the mid-range SCIEX Triple Quad™ 5500+ LC-MS/MS System – QTRAP® Ready or high-end SCIEX Triple Quad™ 6500+ LC-MS/MS System. Both these instruments have detector technology that allows a single method with positive/negative ion switching to run without compromising your data quality.

In the past, MRM conditions were optimized by choosing dwell times that wouldn’t affect the duty cycle of the experiment—which reduced sensitivity and affected detection levels. This generally meant, shorter dwell times for a particular MRM would result in lower accuracy in peak detection and a much higher detection limit.

With the new data acquisition architecture, excellent software algorithms, and powerful electronics, both the SCIEX 5500+ and 6500+ systems can reduce the polarity switching time from 50 milliseconds to 5 milliseconds while maintaining performance characteristics. This ultimately gives an analytical chemist the ability to analyze more compounds in the same amount of time!

See it in action with these workflows:

SCIEX 5500+ System

• Mycotoxins and Other Metabolites
• Pesticides and PPCPs in Environmental Water Samples

SCIEX 6500+ System

• Hydrophilic Paralytic Shellfish Toxins
• Potency Analysis in Hemp and Cannabis Products